Warning from Microsoft to the entire Internet: make sure that your digital certificates are at least 1024 bits. As of Oct. 9, 2012, longer key lengths are mandatory for all digital encryption certificates that touch Windows systems.
This means that Internet Explorer will refuse to access websites that do not have RSA keys with minimum lengths of 1024 bits. You won’t be able to exchange encrypted emails, run ActiveX controls or install applications on Windows. This isn’t new, as Microsoft started making announcements about this well over a year ago.